1. Field of the Invention
The present invention relates to electronic parts with an integrally built-in inductor and, more particularly, to electronic parts such as an inductor, an LC resonator, band-pass filter and an LC filter for use in a portable radio equipment, for example.
2. Description of Related Art
FIG. 7 is an equivalent circuit diagram showing one example of an LC filter acting as a band-pass filter to which the present invention can be applied. The LC filter includes two LC resonators R1 and R2. One LC resonator R1 comprises a first inductor L1 and a first capacitor C1 connected in parallel, and the other LC resonator R2 comprises a second inductor L2 and a second capacitor C2 connected in parallel. It is noted that the first and second inductors L1 and L2 are electromagnetically coupled to each other. One end of the first LC resonator R1 is connected to a first input/output terminal T1 via a third capacitor C3 and one end of the second LC resonator R2 is connected to a second input/output terminal T2 via a fourth capacitor C4. Other ends of the first and second LC resonators R1 and R2 are connected to ground terminals G, respectively.
FIG. 8 is an exploded perspective view showing a main part of the exemplary prior art LC filter having the equivalent circuit shown in FIG. 7. The prior art LC filter 1 shown in FIG. 8 includes four dielectric layers 2a, 2b, 2c and 2d to be laminated together. A first capacitor electrode 3a and the like is formed on the upper surface of the first dielectric layer 2a, a second capacitor electrode 3b and the like is formed on the upper surface of the second dielectric layer 2b and a spiral pattern electrode 4 which acts as an inductor element is formed on the upper surface of the third dielectric layer 2c, the first, second and third electrodes 3a, 3b and 3c being formed of printing conductors by means of thick film printing. The first capacitor C1 of the first LC resonator R1 is formed between the first and second capacitor electrodes 3a and 3b and the first inductor L1 of the first LC resonator R1 is formed by the spiral pattern electrode 4. Similarly, the second capacitor C2 of the other LC resonator R2 is formed between other two capacitor electrodes (not shown) on either side of the second dielectric layer 2b, and the second inductor L2 of the second LC resonator R2 is formed by another pattern electrode (not shown) formed on the upper surface of the third dielectric layer 2c. It is noted that external electrodes (not shown) which act as the input/output terminals T1 and T2 and the ground terminals G are formed on side faces of the dielectric layers 2a through 2d. Further, the third and fourth capacitors C3 and C4 are formed by other capacitor electrodes (not shown) between one end of each of the LC resonators R1 and R2 and the external electrodes which act as the input/output terminals T1 and T2, respectively. The other ends of the LC resonators R1 and R2 are connected to the external electrodes which act as the ground terminals G.
Because each capacitor, which is relatively close to an ideal capacitor, is created in the prior art LC filter 1 shown in FIG. 8, the Q (quality factor) of the whole is influenced largely by the Q of the built-in inductor. Therefore, in order to improve the Q of the LC filter 1, it is conceivable to improve the Q of the inductor by increasing a sectional area of the pattern electrode which acts as the inductor element. It is then conceivable to thicken a width of the pattern electrode in order to increase the sectional area of the pattern electrode, because a thickness of the pattern electrode formed by means of thick film printing is only about 10-odd mm. However, the prior art LC filter has had a problem in that when the width of the pattern electrode is thickened, a value of inductance generated by the pattern electrode made within an equal area becomes small and a large floating capacity is generated between the electrodes similar to the capacitor electrodes which vertically face each other. The result is a drop in Q, contrary to the purpose of the design modification. It is noted that this kind of problem also exists in other built-in inductor electronic parts such as prior art inductors and LC resonators in which a pattern electrode acts as an inductor element and is formed by means of thick film printing.
The prior art LC filter 1 shown in FIG. 8 also has had a problem that although the Q of the whole is improved when the space between the pattern electrode and the vertically disposed capacitor electrode is widened, a thickness of the whole, i.e. the size thereof, is increased and it cannot be mounted within small equipment such as portable radio equipment whose thickness is limited. It is noted that this kind of problem also exists in the other inductor built in electronic parts such as prior art LC resonators in which the pattern electrode which acts as an inductor element and the capacitor electrode are formed, respectively, by means of thick film printing.
Further, the LC filter 1 shown in FIG. 8 has had a problem in that because a line of magnetic force generated by the pattern electrode crosses with the main surface of the capacitor electrode at almost right angles as shown in FIG. 9, a significant eddy current loss is generated on the capacitor electrode by the line of magnetic force, thus dropping the Q of the whole. It is noted that this kind of problem also exists in the other built-in inductor electronic parts such as the prior art LC resonator in which the pattern electrode which acts as an inductor element and the capacitor electrode are formed, respectively, by means of thick film printing.
Accordingly, it is a primary object of the present invention to provide a small built-in inductor electronic parts whose Q is high.